Disk array devices, such as for example, a RAID (Redundant Arrays of Inexpensive Disk) set, have become popular. The RAID storage unit secures data reliability as an entire system with a data redundancy configuration established among disks in a RAID group consisting of a plurality of the disks (see, for example, Japanese Laid-open Patent Publication No. 2002-222063 and No. 2009-116783).
Even if a failure occurs in some disks in the RAID group and a fallback occurs in the data redundancy of the RAID group, the RAID storage unit can cause the data content stored in the failed disk(s) to be restored in a destination disk, such as a spare disk and a replaced normal disk. A widely used restoration process is, for example, a data reconstruction process (hereinafter, referred to as a “rebuild process”).
Thus, even if a failure occurs in some disks and a fallback occurs in the data redundancy in the RAID group, the RAID storage unit can recover the redundancy through the rebuild process to cause the data content in the failed disk to be restored in the destination disk.
In particular, in the rebuild process, the data content stored in the failed disk is sequentially restored from the first block to the last block of the actual storage space with reference to the failed disk and disks other than the failed disk in the RAID group.
In the rebuild process, the data content of the failed disk can be reconstructed and restored in the destination disk by sequentially storing the restored data in the actual storage space in the destination disk.
Upon detection of a write request issued by a host for new data with respect to a virtual volume to be accessed, the RAID storage unit allocates, as the virtual volume, a logical volume corresponding to an actual storage space of the disk which exists in the same RAID group in accordance with the volume capacity of the new data.
The virtual volume is not allocated from the actual storage space during creation of the logical volume recognized by the host, but allocated sequentially from the actual storage space corresponding to a range of an I/O request upon detection of an I/O request of a write request issued by the host. The RAID storage unit causes the new data of the write request to be stored as the actual data in the actual storage space of the disk corresponding to the logical storage space allocated to the virtual volume.
FIG. 14 illustrates a relationship between a logical storage space and an actual storage space of the RAID groups when a virtual volume is used.
The virtual volume randomly includes, in the actual storage space in the RAID group, stored spaces in which the actual data is stored and spaces in which no actual data is stored (i.e., a zero data space).
In a rebuild process for a virtual volume in related art RAID storage units, data in the actual storage space of the failed disk is sequentially restored from the first block to the last block and the restored data is reconstructed in the actual storage space in the destination disk. Thus, in the related art RAID storage units, since the data content stored in the actual storage space of the failed disk is caused to be restored in the actual storage space of the destination disk, the data redundancy in the RAID group can be recovered.
In such related art RAID storage units, data in the first block to the last block of the destination disk is uniformly reconstructed irrespective of the concept of the stored space in which the actual data has been stored and the space in which no data is stored in the actual storage space of the failed disk. Recently, disks with increasingly larger storage capacity are being developed.
The related art RAID storage units require significantly long time to restore data uniformly and sequentially from the first block to the last block in the disk of large capacity and reconstructs the data content in the destination disk. It therefore takes long time to recover data redundancy in the RAID group.